Forest carbon stocks have been overestimated for 50 years

For more than 70 years, CIRAD has had a database on 1300 wood species and almost 4500 trees. It was when they came to promote this resource that Ghislain Vieilledent and his colleagues at CIRAD and at Paul Sabatier University in Toulouse discovered an incoherence in a conversion factor: the one used to compute the basic density of a tree based on wood density at 12% moisture, which corresponds to the average wood moisture content in temperate regions. Since this technical characteristic is widely available in wood technology databases, ecologists only have to apply a conversion factor to it in order to establish the basic density of a tree species. However, it was precisely that conversion factor that did not tally with the researchers' new calculations. "To start with, I thought we had made a mistake in our calculations or that there was some uncertainty surrounding measurement of the relevant data. It was not easy to cast doubt on a formula that had been widely accepted for years and quoted in several scientific articles."

The researchers took a new look at the data in CIRAD's historic database in order to determine a new formula for establishing basic density based on density at 12%. The new conversion factor will be used to calculate the basic density of woods in forest ecology databases. In particular, it will serve to update the global wood density database on which Jérôme Chave and Fabian Fischer are working at CNRS-Paul Sabatier University in Toulouse, who were co-authors of the publication. The correction will make it possible to estimate carbon forest stocks more accurately and understand more clearly the role played by forests in climate regulation.